A multicolor light-emitting device is proposed in which a plurality of light-emitting devices are stacked (U.S. Pat. No. 5,707,745). In the multicolor light-emitting device disclosed in this document, the stacked light-emitting devices are divided from each other by a transparent electroconductive layer so that each light-emitting device can be individually driven. When having three layers of emission layers stacked therein, for instance, the multicolor light-emitting device results in having a structure in which a first emission layer is sandwiched between a first electrode and a second electrode, a second emission layer is sandwiched between the second electrode and a third electrode, and a third emission layer is sandwiched between the third electrode and a fourth electrode. The multicolor light-emitting device also has a structure in which three power sources for individually driving the three layers of the emission layers are connected to the respective layers, and the power sources are connected in series because the second electrode and the third electrode are common between upper and lower emission layers.
An active matrix type electroluminescence display apparatus using a TFT is known. In the electroluminescence display apparatus, the light-emitting luminance of the device is controlled by an electric current, and a TFT for controlling the electric current and a switching TFT for selecting a pixel are arranged in each pixel. The driving voltage per one layer of a general organic electroluminescence device is approximately 5 V, and the threshold Vth of the TFT is approximately 2 V.
When the structure in the above described document is formed to be the active matrix type, it is assumed that three pixel circuits are provided in one pixel. Specifically, three current control TFTs and three switching TFTs are arranged in one pixel. A case will now be described below in which the current control TFT is an n-type and the first electrode is connected to GND.
When all three layers of the first, second and third emission layers are turned off, 0 V is applied to the gates of all current control TFTs. When making all of the three layers of the first, second and third emission layers emit light, 7 V including the threshold Vth is applied to the gate of the current control TFT for the first emission layer. Similarly, 12 V is applied to the gate of the current control TFT for the second emission layer, and 17 V is applied to the gate of the current control TFT for the third emission layer. This is because the potential difference between the first electrode and the fourth electrode is 15 V at the maximum, though a potential difference to be applied to each of the emission layer is 5 V.
Accordingly, the data signal voltage for controlling the current control TFT is in a range from 0 V to 17 V. The data signal voltage is applied to through the switching TFT for selecting a pixel, so that the switching TFT needs to have a withstand voltage of 17 V between the source and the drain.
Generally, the TFT to be formed on a glass substrate has a withstand voltage of 10 V to 15 V between the source and the drain. Therefore, when the structure in the above described document is formed to be the active matrix type, the structure causes a problem that the voltage applied to between the source and the drain of the switching TFT exceeds its withstand voltage.